JP2017223871A - Image forming apparatus and method for controlling the same, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that in a conventional technique, to calculate a pixel to be corrected and a toner amount, it is necessary to calculate a difference between an original image and an image obtained by shifting the original image several times, the processing of which is complicated, and because density over the whole image is corrected, density in a portion in which the toner amount is not excessive is changed by an edge effect.SOLUTION: An image forming apparatus has a photoreceptor, an exposure device which irradiates the photoreceptor with light based on an exposure signal to form an electrostatic latent image on the photoreceptor, and control means which supplies the exposure signal to the exposure device, where the control means executes filter processing of input image data, detects a pixel of which a toner amount after development exceeds a prescribed amount and its amount by an edge effect or sweeping phenomenon, creates thinning-out information for determining a pixel of which the toner amount is to be reduced and an amount to be reduced based on the detected result, creates image data obtained by imparting the thinning-out information to the image data, and creates an exposure signal based on the created image data.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus, a control method thereof, and a program.

  In an image forming apparatus that forms an image by an electrophotographic method, reduction of toner consumption is eagerly desired. In relation to this toner consumption amount, there is a phenomenon called “sweeping” in which the toner amount for developing the rear end portion of the latent image becomes larger than the toner amount in the latent image plane portion. For example, Patent Document 1 corrects the toner amount at the trailing edge of the latent image by correcting the image data to adjust the exposure amount of the pixel portion where the toner amount becomes excessive due to the sweeping phenomenon. The technology to do is described.

  On the other hand, there is a phenomenon similar to sweeping, a phenomenon called edge effect, in which the amount of toner that develops the latent image edge is greater than the amount of toner in the latent image plane. For example, Patent Document 2 proposes a technique for correcting the density of the entire image against this phenomenon.

Japanese Patent No. 4898259 Japanese Patent No. 5453327

  However, in the former technique for correcting the sweeping, it is necessary to calculate the difference between the original image and the shifted image several times in order to calculate the pixel to be corrected and the toner amount, and the processing is complicated. It is.

  Further, in the latter technique for correcting the edge effect, the processing is not complicated because pixels that use an excessive amount of toner for development are not detected. However, since the density correction is performed over the entire image, there is a problem that the density of the portion where the toner amount is not excessive changes due to the edge effect.

  An object of the present invention is to solve the above-described problems of the prior art.

  An object of the present invention is to provide a technique capable of determining a pixel in which the amount of toner is excessive due to an edge effect or a phenomenon of sweeping, and the amount thereof, and reducing the amount of toner only for pixels in which the toner amount is excessive. is there.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention has the following configuration. That is,
Image formation comprising: a photoconductor; an exposure device that irradiates the photoconductor with light based on an exposure signal to form an electrostatic latent image on the photoconductor; and a control unit that supplies the exposure signal to the exposure device A device,
The control means includes
A detection means for executing a filtering process on the input image data and detecting a pixel and a toner amount after development exceeding a predetermined amount due to an edge effect or a phenomenon of sweeping;
Based on the detection result of the detection means, create thinning information for determining the pixel to be reduced in toner amount and the amount to be reduced, and create image data with the thinning information added to the image data Creating means to
Generating means for generating the exposure signal based on the image data created by the creating means.

  According to the present invention, it is possible to determine a pixel in which the toner amount is excessive due to an edge effect or a phenomenon of sweeping, and the amount thereof, and to perform a correction process for reducing the toner amount only for the pixel in which the toner amount is excessive. it can.

  Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are denoted by the same reference numerals.

The accompanying drawings are included in the specification, constitute a part thereof, show an embodiment of the present invention, and are used together with the description to explain the principle of the present invention.
1 is a block diagram illustrating a basic configuration of an electrophotographic image forming apparatus according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a functional configuration of a controller of the image forming apparatus according to the embodiment. FIG. 6 is a diagram for explaining how the exposure apparatus is controlled by the exposure control unit and the exposure drive unit of the image forming apparatus according to the embodiment. FIG. 6 is a diagram for explaining a method of adjusting image density by PWM control using a drive signal output from an exposure drive unit of the image forming apparatus according to the embodiment. FIG. 4 is a diagram illustrating an example of a multi-valued image stored in an image memory of the image forming apparatus according to the embodiment. FIG. 6 is a diagram illustrating an example of a binary image generated by performing image processing on the image of FIG. 5 by a density conversion unit and a halftone conversion unit. FIG. 5 is a diagram illustrating an example of filter coefficients used by the thinning information generation unit of the image forming apparatus according to the embodiment for filter image processing. FIG. 7 is a diagram illustrating image data (toner applied amount) generated by performing filter image processing on the binary image data illustrated in FIG. 6 by a thinning information generation unit. FIG. 9 is a diagram showing thinning information corresponding to data indicating the applied toner amount shown in FIG. 8. FIG. 7 is a diagram illustrating an example of binary image data with thinning information obtained by adding thinning information to the image of FIG. 6. FIG. 11 is a schematic diagram showing an electrostatic latent image formed on the surface of the photosensitive drum when the binary image data with thinning information shown in FIG. 10 is used. FIG. 7 is a diagram illustrating an example of an excessive amount of toner when the binary image data illustrated in FIG. 6 is developed by directly forming an electrostatic latent image without performing a thinning process by PWM control. 6 is a flowchart for describing processing for creating a filter coefficient used when the image forming apparatus according to the embodiment generates thinning information. The figure which shows an example of the one-dimensional filter coefficient produced | generated when creating the filter coefficient used when producing | generating thinning-out information in embodiment. FIG. 6 is a diagram illustrating a relationship between a toner loading amount t and thinning information according to the embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. . First, the basic operation of the electrophotographic image forming apparatus according to the embodiment will be described.

  FIG. 1 is a block diagram illustrating a basic configuration of an electrophotographic image forming apparatus 100 according to an embodiment of the present invention.

  The image forming apparatus 100 includes a photosensitive drum 110, a charger 120, an exposure device 130, a controller (control unit) 140, a developing device 150, a transfer roller 160, and a fixing device 170. The hatched portion of the developing device 150 represents toner that is a developer. Further, R on the photosensitive drum 110 represents a development area, T represents a transfer position, and P represents a recording medium (paper). A portion that performs an operation related to image formation excluding the controller 140 in the image forming apparatus 100 is referred to as a printer engine.

  The photosensitive drum 110 is a drum-shaped electrophotographic photosensitive member that functions as an image carrier. The charger 120 has a charging roller, and uniformly charges the surface of the photosensitive drum 110. The exposure device 130 is an exposure unit that exposes a uniformly charged photosensitive drum 110 by irradiating an amount of laser light based on image data, and has a laser beam scanner. This exposure is performed by a laser beam, and an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 110 by this exposure. That is, the photosensitive drum 110 is irradiated with light according to the exposure signal output from the controller 140 to form an electrostatic latent image.

  The controller 140 outputs to the exposure apparatus 130 the above-described drive signal and a light amount adjustment signal for driving the semiconductor laser to adjust the target light amount at the time of exposure. By this light quantity adjustment signal, a constant amount of current is supplied to the exposure apparatus 130, and the exposure intensity is controlled to be constant. By adjusting the light amount for each pixel with the target light amount as a reference, or adjusting the light emission time by pulse width modulation, the gradation expression of the image is realized. In addition, the controller 140 performs correction processing on the raster image data transmitted from the host computer 10 to suppress excessive toner adhesion due to the edge effect or the sweeping phenomenon and reduce the toner consumption. Details thereof will be described later.

  The developing device 150 includes a toner container that stores and stores toner, a developing roller 151 that is a developer carrier, and a regulating blade 152 that functions as a toner layer thickness regulating member. Here, a non-magnetic one-component toner is used as the toner, but a two-component toner or a magnetic toner may be used. The layer thickness of the toner supplied to the developing roller 151 is regulated by the regulation blade 152 described above. The regulating blade 152 may be configured to apply a charge to the toner. Then, the toner which is regulated to a predetermined layer thickness and to which a predetermined amount of charge is applied is conveyed to the developing region R by the developing roller 151. The development region R is a region where the developing roller 151 and the photosensitive drum 110 are close to or in contact with each other and toner is attached thereto. The electrostatic latent image formed on the surface of the photosensitive drum 110 is developed with toner and converted into a toner image. The toner image thus formed on the surface of the photosensitive drum 110 is transferred to the recording medium P by the transfer roller 160 at the transfer position T. The recording medium P onto which the toner image has been transferred is conveyed to the fixing device 170. The fixing device 170 applies heat and pressure to the toner image and the recording medium P to fix the toner image on the recording medium P.

  FIG. 2 is a block diagram illustrating a functional configuration of the controller 140 of the image forming apparatus 100 according to the embodiment. Hereinafter, the operation of the controller 140 will be described together with related peripheral devices.

  The controller 140 includes a CPU 210, a ROM 220, a RAM 230, an exposure control unit 240, an exposure drive unit 250, an image processing unit 260, and a host I / F 270, which are connected to each other via a bus 280. The host I / F 270 is an interface for exchanging data with the host computer 10. The CPU 210 transmits a control signal to each part of the image forming apparatus 100 according to a program code stored in advance in the ROM 220, and receives a signal from each part to control the operation of the entire image forming apparatus 100. The ROM 220 stores a program code for the CPU 210. In addition, the ROM 220 indicates a correction target that indicates whether correction for the edge effect or correction for sweeping is performed when correction processing for reducing the toner amount is performed on a pixel whose toner amount is excessive. Information on the phenomenon is stored in advance. In general, the correction for the edge effect or the correction for sweeping is set based on the development method, jumping development method, contact development method, or the like fixedly determined by the configuration of the printer engine. Further, the ROM 220 provides information on a phenomenon in which the toner is excessively applied to the edge of the latent image due to the edge effect or sweeping, specifically, the pixel having the maximum toner amount and the pixel having the toner amount in the standard range. Information on the distance from the edge of the image is stored in advance. The description about the distance from the image edge part of these pixels is mentioned later.

  The RAM 230 is a memory that functions as a work area of the CPU 210, and has an image memory 231 as a part of the memory area. The image memory 231 is a storage area (page memory, line memory, etc.) in which image data to be subjected to image formation is expanded. The RAM 230 also stores an LUT (Look Up Table) that stores correction parameters (pixel width to be corrected), correction coefficients (exposure reduction ratio), and the like.

  The exposure control unit 240 executes APC (automatic light amount control) on the light source of the exposure apparatus 130 to set a target light amount, and generates the light amount adjustment signal 211 described above. The exposure driving unit 250 receives binary image data with thinning information stored in the image memory 231 under the control of the CPU 210, adjusts the image density by PWM (pulse width modulation) control, and the exposure device 130. A drive signal 212 for driving is generated and output. In the PWM control, when the pixel value is “0”, a value of a drive signal on which toner is not applied is output, and when the pixel value is “1”, a predetermined PWM pattern corresponding to the thinning information of the pixel is driven. It is output as a signal. Details of a method of outputting a predetermined PWM pattern corresponding to the thinning information as a drive signal will be described later.

  The image processing unit 260 includes a density conversion unit 261, a halftone conversion unit 262, a delay unit 263, a thinning information generation unit 264, and a thinning information addition unit 265. The image processing unit 260 operates under the control of the CPU 210, converts multi-valued image data stored in the image memory 231 into binarized image data, and generates thinning information from the binary image data. The image data is added to the image data and output to the image memory 231. The density conversion unit 261 receives multivalued image data stored in the image memory 231, converts the luminance signal into a density signal, and outputs the converted signal. The halftone conversion unit 262 receives the multivalued image data output from the density conversion unit 261, converts it into binary image data, and outputs it. As the halftone conversion method, an algorithm using a dither method or an error dispersion method is known, but detailed description thereof is omitted. The delay unit 263 receives the binary image data output from the halftone conversion unit 262 and outputs it after a predetermined time. The predetermined time is the same time as the time when the thinning information generation unit 264 generates the thinning information. The delayed binary image data is sent to the thinning information addition unit 265 by the thinning information generation unit 264. In contrast, it is synchronized with the thinned data output. The thinning information generation unit 264 receives the binary image data output from the halftone conversion unit 262, generates thinning information, and outputs it. Details of the method of generating the thinning information will be described later. The thinning information addition unit 265 receives the binary image data output from the delay unit 263 and the thinning data output from the thinning information generation unit 264 and arranges the data alternately for each pixel. Thus, binary image data with thinning information is generated and output to the image memory 231.

  FIG. 3 is a diagram for explaining how the exposure apparatus 130 is controlled by the exposure control unit 240 and the exposure driving unit 250 of the image forming apparatus 100 according to the embodiment.

  The exposure control unit 240 includes an IC 241 that incorporates an 8-bit DA converter 2021 and a regulator (REG) 2022, generates the light amount adjustment signal 211 described above, and sends it to the exposure apparatus 130. The exposure apparatus 130 includes a VI conversion circuit 131 that converts voltage into current, a laser driver IC 132, and a semiconductor laser 133.

  The IC 241 of the exposure control unit 240 adjusts the light amount adjustment signal 211 based on the voltage VrefH output from the regulator 2022 based on the base signal indicating the drive current of the semiconductor laser 133 set by the CPU 210 of the controller 140. Here, the voltage VrefH is a reference voltage for the DA converter 2021. In this way, the analog voltage for light amount adjustment as the light amount adjustment signal 211 is output from the DA converter 2021 of the IC 241.

  The VI conversion circuit 131 of the exposure apparatus 130 converts the light amount adjustment signal 211 received from the exposure control unit 240 into a current value Id and outputs it to the laser driver IC 132. Here, the IC 241 mounted on the exposure control unit 240 outputs the light amount adjustment signal 211. However, a DA converter may be mounted on the exposure apparatus 130 to generate a light amount adjustment signal in the vicinity of the laser driver IC 132.

  The laser driver IC 132 switches the switch SW in accordance with the drive signal 212 output from the exposure drive unit 250. The switch SW controls ON / OFF of light emission of the semiconductor laser 133 by switching whether the current IL is supplied to the semiconductor laser 133 or the dummy resistor R1.

  FIG. 4 is a diagram illustrating a method for adjusting the image density by PWM control using the drive signal 212 output from the exposure drive unit 250 of the image forming apparatus 100 according to the embodiment.

  In FIG. 4, PWM0 to PWM8 respectively indicate PWM patterns formed by dividing one pixel into 16 subpixels (subpixels) and thinning out some subpixels. The exposure driving unit 250 controls the drive signal so that the toner is placed on the black subpixel portion, and controls the drive signal so that the toner is not placed on the white subpixel portion. Adjust. The percentage values in the figure indicate the pixel density corresponding to each PWM pattern (PWM0 to PWM8), PWM0 is 100%, and PWM1 to PWM8 correspond to 93.75% to 50.00%, respectively. These are the concentrations shown in the figure. The exposure driving unit 250 outputs, for each pixel of the received binary image data with thinning information, a value of a driving signal on which toner is not placed when the pixel value is “0”. When the pixel value is “1”, a predetermined PWM pattern corresponding to the thinning information given to the pixel is output as a drive signal. Here, the PWM pattern corresponding to the decimation information is PWM0 when the decimation information value is “0”, PWM1 when the decimation information value is “1”, PWM8 when “8”, and so on. A PWM pattern is selected according to the value of the thinning information. The value of the thinning information is “0” to “8”. As described above, the exposure driving unit 250 controls the pixel density by thinning the exposure light amount by PWM control using the drive signal 212.

  FIG. 5 is a diagram illustrating an example of a multi-valued image stored in the image memory 231 of the image forming apparatus 100 according to the embodiment.

  The number of pixels of this image is 32 pixels in the main scanning direction (horizontal direction) and 32 pixels in the sub-scanning direction (vertical direction), and the pixel values are “255” for white pixels and “0” for black pixels.

  FIG. 6 is a diagram illustrating an example of a binary image generated by performing image processing on the image in FIG. 5 by the density conversion unit 261 and the halftone conversion unit 262.

  FIG. 6A is a diagram illustrating the appearance of a binary image. In this example, the appearance of the original image and the image shown in FIG. 5 is not changed, but the pixel value is changed by the image processing of the density conversion unit 261 and the halftone conversion unit 262, white pixels are “0”, and black pixels are “1”. ".

  FIG. 6B is a graph showing the image data of FIG. 6A in three dimensions. In FIG. 6B, the value of the black pixel portion is represented by “1”, and the other pixel portions are represented by “0”.

  FIG. 7 is a diagram illustrating an example of filter coefficients used by the thinning information generation unit 264 for the filter image processing according to the embodiment. Here, since the filter coefficient is set so that the result of the filter image processing can be regarded as the amount of applied toner, the image data of the result of the filter image processing is called toner applied amount data.

  FIG. 7A is a diagram illustrating an example of a filter coefficient for detecting a pixel in which the toner amount is excessive due to the phenomenon of the edge effect. The central square is a coefficient (here, “1.00”) corresponding to the target pixel of the filter image processing, and the peripheral square is a coefficient corresponding to the peripheral pixel of the filter processing.

  FIG. 7B is a diagram illustrating an example of a filter coefficient for detecting pixels in which the toner amount is excessive due to the sweeping phenomenon. Again, the central square is a coefficient (here, “1.00”) corresponding to the target pixel of the filter image processing, and the peripheral square is a coefficient corresponding to the peripheral pixel of the filter processing.

  FIG. 7C is a graph showing the filter coefficients of FIG. 7A in three dimensions. The coefficient corresponding to the peripheral pixels up to a certain distance centered on the coefficient (1.00) corresponding to the target pixel is a positive number. The coefficient corresponding to the peripheral pixels up to another certain distance outside thereof is a negative number, and the coefficient corresponding to the peripheral pixels outside thereof is “0”. The thinning-out information generation unit 264 performs two-dimensional convolution on the received binary image data in order to detect a pixel in which the toner amount is excessive due to an edge effect or a sweeping phenomenon, and the degree of excess. Performs filter image processing by sum calculation. Image data obtained as a result of this filter image processing, that is, a pixel having a value exceeding “1” in the applied toner amount data is a pixel in which the toner amount is excessive. The thinning information generation unit 264 determines thinning information for each pixel of the applied toner amount data with reference to a table (FIG. 15) that associates the applied toner amount with the thinned information. Through the above procedure, the thinning information generation unit 264 generates thinning information corresponding to each pixel of the input binary image data, and outputs the thinning information to the thinning information addition unit 265.

  FIG. 15 is a diagram illustrating a relationship between the toner loading amount t and the thinning information according to the embodiment.

  FIG. 8 is a diagram showing image data generated by performing the filter image processing on the binary image data shown in FIG.

  FIG. 8A is a three-dimensional representation of the applied toner amount when the filter coefficient of FIG. 7A is used, and the applied toner amount exceeds “1” due to the phenomenon of the edge effect. A pixel is generated.

  FIG. 8B is a three-dimensional representation of the applied toner amount when the filter coefficient of FIG. 7B is used, and the applied toner amount exceeds “1” due to the phenomenon of sweeping. A pixel is generated.

  FIG. 9 is a diagram showing thinning information corresponding to the data indicating the applied toner amount shown in FIG. 8, and FIG. 9A shows thinning for the phenomenon of edge effect corresponding to FIG. 8A. FIG. 9B shows thinning information corresponding to the sweeping phenomenon corresponding to FIG. 8B.

  FIG. 10 is a diagram illustrating an example of binary image data with thinning information obtained by adding thinning information generated by the thinning information generation unit 264 by the thinning information addition unit 265 to the image of FIG. is there.

  FIG. 10A shows binary image data with thinning information obtained by adding the thinning information of FIG. 9A to the image of FIG. 6, and FIG. 10B shows the image of FIG. FIG. 9 is a diagram illustrating an example of binary image data with thinning information to which thinning information is added.

  FIG. 11 is a schematic diagram showing an electrostatic latent image formed on the surface of the photosensitive drum 110 when the binary image data with thinning information shown in FIG. 10 is used.

  As described above, under the control of the CPU 210, the exposure driving unit 250 receives binary image data with thinning information stored in the image memory 231 and outputs the driving signal 212, and the exposure device 130 receives the photosensitive drum. An electrostatic latent image is formed on the surface of 110. In FIG. 11, the pixel portion where the toner is not placed is represented in white, and the pixel portion where the toner is placed is represented in black. In addition, the pixels that are thinned out by PWM control are actually thinned out in units of sub-pixels as shown in FIG. 4 to adjust the density. In FIG. 11, the density according to the degree of thinning is adjusted. , Schematically represented by shading.

  FIG. 11A is a schematic diagram showing an electrostatic latent image when binary image data with thinning information added with thinning information in FIG. 10A is used. It can be confirmed that due to the phenomenon of the edge effect, pixels whose toner amount becomes excessive after the development are targeted for thinning.

  FIG. 11B is a schematic diagram showing an electrostatic latent image when binary image data with thinning information added with thinning information in FIG. 10B is used. Due to the phenomenon of sweeping, it can be confirmed that pixels whose toner amount becomes excessive after development are the targets of thinning.

  FIG. 12 shows an example of an excessive amount of toner when the binary image data shown in FIG. 6 is developed by directly forming an electrostatic latent image without performing the thinning process by PWM control. FIG. The exposure driving unit 250 can also receive binary image data without thinning information. In this case, the exposure driving unit 250 operates without thinning processing, but measures the amount of toner developed in this operation. Thus, the graph shown in FIG. 12 can be created.

  FIG. 12A is a diagram showing the toner amount due to the phenomenon of the edge effect. When the amount of toner that develops the central portion of the image in the sub-scanning direction shown in FIG. 6 in the main scanning direction is measured, the edge effect phenomenon that the toner amount at the edge of the latent image becomes excessive causes the vicinity of the edge of the black image. It can be seen that a lot of toner is on. In this example, the pixel position where the toner amount is maximum is 3 pixels inside the edge of the image, and the toner amount is within the standard range 7 pixels inside the edge of the image. . Here, the standard range of the toner amount is a range indicated by oblique lines in FIG. 12, and is a range having a slight width with reference to the toner amount of the latent image flat portion.

  The thinning information according to the present embodiment is generated by detecting a pixel on which an excessive amount of toner is placed outside the standard range. Therefore, if the width of the standard range is changed, it is recognized that the toner amount is excessive. The threshold value to be changed is also changed. This is realized by reflecting the two distances from the edge of the image measured here, that is, the values of 3 pixels and 7 pixels in the filter coefficient used when generating the thinning information. To do. It should be noted that the two distances obtained here, 3 pixels and 7 pixels, are stored in the ROM 220 described above from the edge of the image for each of the pixels with the maximum toner amount and the pixels with the toner amount within the standard range. Is stored as distance information.

  FIG. 12B illustrates the amount of toner due to the phenomenon of sweeping. When the toner amount for developing the central portion of the image in the main scanning direction shown in FIG. 6 in the sub-scanning direction is measured, the vicinity of the rear end portion of the image is caused by the phenomenon of sweeping that the toner amount at the rear end portion of the latent image becomes excessive It can be seen that a large amount of toner is loaded. In this example, the pixel position where the toner amount is maximum is 3 pixels inside the rear end of the image, and the toner amount is within the standard range 7 pixels inside the rear end of the image. is there. The two distances obtained here, the values of 3 pixels and 7 pixels are stored in the ROM 220 described above, and the distance from the image edge of each of the pixels with the maximum toner amount and the pixels with the toner amount within the standard range. It memorizes as information.

  Here, the position and amount where the toner amount becomes excessive and whether the edge effect or the sweeping phenomenon occurs depends on operating conditions such as the characteristics and speed of the printer engine. For this reason, it is desirable to perform measurement according to the actual operating conditions of the printer engine. If it is difficult to measure the amount of developed toner, a large amount of lines with the same line width are printed. The amount of toner consumed at this time is measured, and the amount of developed toner can be determined based on how much the toner is consumed more than the ideal amount of toner consumed. By investigating this with respect to lines having several line widths, it is estimated that the toner is excessively developed due to the edge effect and the phenomenon of sweeping. It is also possible to estimate the distance from the image edge of each of the pixel having the maximum toner amount and the pixel having the toner amount in the standard range.

  FIG. 13 is a flowchart illustrating processing for creating a filter coefficient used when the image forming apparatus 100 according to the embodiment generates thinning information. This processing may be performed by the CPU 210 executing a program stored in the ROM 220, or may be executed in advance by a PC or the like and the obtained filter coefficients may be stored in the ROM 220 or the like. Therefore, the following description of each processing step is described as control of the CPU 210 in the embodiment, but may be executed by another device or the like.

  In step S <b> 1301, the CPU 210 reads information on a phenomenon to be corrected stored in the ROM 220 and determines whether the phenomenon to be corrected is an edge effect or a sweeping effect. If the phenomenon to be corrected is an edge effect, the process proceeds to S1302, and if it is swept, the process proceeds to S13055.

  In S <b> 1302, the CPU 210 reads distance information from the image end of the pixel with the maximum toner amount and the pixel with the toner amount within the standard range from the information stored in the ROM 220, and proceeds to S <b> 1303. In S1303, the CPU 210 first generates a one-dimensional filter coefficient so as to satisfy the constraints described later, and proceeds to S1304. One of the restrictions is that the filter coefficient of the target pixel is “1”. Further, one of the restrictions is that the filter coefficient of a pixel having the maximum toner amount counted from the target pixel and separated by the same distance (number of pixels) as the distance from the image edge (3 pixels) is “ “0” means that the inner filter coefficient is a positive number less than “1”. In addition, one of the restrictions is that the pixel whose toner amount is within the standard range from the target pixel is the same distance (number of pixels) as the distance from the image edge (7 pixels), and a pixel that is more than that. The filter coefficient is “0”. And the filter coefficient except the thing fixed by the above-mentioned restrictions inside is a negative number larger than "-1". An example of the one-dimensional filter coefficient generated in S1303 is shown in FIG.

  FIG. 14 is a diagram illustrating an example of a one-dimensional filter coefficient generated when creating a filter coefficient used when generating thinning information in the embodiment.

  FIG. 14A shows an example of the one-dimensional filter coefficient generated in S1303.

  In FIG. 14A, the filter coefficients 1401 and 1402 that are separated from the target pixel 1400 by the same distance (number of pixels) as the distance (three pixels) from the image end of the pixel having the maximum toner amount are “ 0 ". The inner filter coefficient is a positive number less than “1” (“0.10” and “0.30” in FIG. 14A). Also, the filter coefficients 1403 and 1404 that are separated from the target pixel 1400 by the same distance (number of pixels) as the distance from the image edge (7 pixels) of the pixel whose toner amount is in the standard range are “0”. . Then, on the inside, the filter coefficients excluding those determined by the above-described constraints are negative numbers larger than “−1” (in the figure, “−0.03”, “−0.04”, “−0.03”). ).

  Next, proceeding to S1304, the CPU 210 generates a two-dimensional filter coefficient to satisfy a later-described constraint based on the one-dimensional filter coefficient obtained in S1303, and ends this process. One of the constraints is that the distance from the target pixel is calculated for each of the two-dimensional filter coefficients, and two adjacent coefficients closest to the distance are selected from the one-dimensional filter coefficients generated in S1303. The coefficient value is calculated by linear interpolation. By determining the filter coefficient value based on the distance from the pixel of interest in this way, the maximum number of filter coefficient values is 24, and in the example of the filter coefficient of this embodiment, 11 types are compared with the total number of filter coefficients. The number of types can be greatly reduced. Thereby, the calculation of the filter image processing by the calculation of the two-dimensional convolution sum by the thinning information generation unit 264 can be optimized. Specifically, the multiplications included in the calculation of the convolution sum of pixels having the same filter coefficient value can be performed together, and the multiplication is performed by calculating the sum of the corresponding pixel values and then multiplying by the filter coefficient value. Can be reduced. As a result, the circuit scale of the hardware logic circuit for filter image processing can be reduced.

  Further, one of the restrictions is that a value obtained by adding all the filter coefficients is “1”. This restriction has an effect that the thinning information of the flat portion becomes “0”. Since this constraint depends on the one-dimensional filter coefficient generated in S1302, there is a method of creating a one-dimensional filter coefficient so that the constraint is satisfied in advance. Or, after generating the two-dimensional filter coefficient, the positive coefficient and the negative coefficient of the filter coefficient other than the target pixel are set so that the total sum of the filter coefficient values other than the filter coefficient of the target pixel becomes “0”. There are ways to increase or decrease each separately. In the present embodiment, a one-dimensional filter coefficient is created in advance so that the constraint is satisfied, and the constraint is satisfied. The two-dimensional filter coefficient generated in S1304 is the same as that shown in FIG. 7A, for example.

  Then, as shown in FIG. 9A, by generating the thinning information using the filter coefficient created in this procedure, the thinning information of the pixel with the maximum toner amount becomes large, and the toner amount The thinning-out information for pixels that fall within the standard range is “0”. Therefore, by generating the filter coefficient in this procedure, it is possible to reduce the toner amount only for the pixels where the toner amount is excessive due to the phenomenon of the edge effect, and further, the reduction amount of the toner amount of the pixel where the toner amount is most excessive is increased. can do.

  On the other hand, if the correction target is a sweeping phenomenon, the process proceeds to step S1305, and the CPU 210 determines from the information stored in the ROM 220 that the pixel with the maximum toner amount and the pixel with the toner amount within the standard range from the end of the image. The distance information is read out and the process proceeds to S1306. In S1306, the CPU 210 generates a one-dimensional filter coefficient so as to satisfy the constraints described later, and proceeds to S1307. One of the restrictions is that the filter coefficient of the target pixel is “1” and the filter coefficient on the left side of the target pixel is “0”. Further, one of the restrictions is that the right filter coefficient is “0” by the same distance (number of pixels) as the distance from the image edge (3 pixels) of the pixel having the maximum toner amount counting from the target pixel. The inner filter coefficient is a positive number less than “1”. Furthermore, one of the restrictions is that the right filter coefficient is set to the right distance (number of pixels) by the same distance (number of pixels) as the distance from the image edge (7 pixels) of the pixel whose toner amount is in the standard range, counting from the target pixel. 0 ”. And the filter coefficient except the thing fixed by the previous restrictions inside is a negative number larger than “−1”. One of the restrictions is that a value obtained by adding all the filter coefficients is “1”. This restriction has an effect that the thinning information of the flat portion becomes “0”. An example of the one-dimensional filter coefficient generated in step S1306 is shown in FIG.

  FIG. 14B is a diagram illustrating an example of the one-dimensional filter coefficient generated in S1306. In FIG. 14B, the right filter coefficient 1405 is “0” by the same distance (number of pixels) as the distance (three pixels) from the image end of the pixel having the maximum toner amount, counting from the target pixel 1400. It is. The inner filter coefficient is a positive number less than “1” (here, “0.90” and “0.40”). The right filter coefficient 1406 is “0” by the same distance (number of pixels) as the distance (7 pixels) from the image end of the pixel whose toner amount is in the standard range, counting from the target pixel 1400. The filter coefficient excluding the one determined by the previous constraint inside is a negative number larger than “−1” (here, “−0.40”, “−0.50”, “−0.40”). To do. A value obtained by adding all the filter coefficients is 1.00 + 0.90 + 0.40−0.40−0.50−0.40 = “1”.

  Next, proceeding to S1307, the CPU 210 generates a two-dimensional filter coefficient so as to satisfy the later-described constraints based on the one-dimensional filter coefficient obtained in S1306, and ends this process. One of the restrictions is to set the one-dimensional filter coefficient generated in S1306 to the filter coefficient in the sub-scanning direction including the target pixel of the two-dimensional filter coefficient, and set all other filter coefficients to “0”. . The two-dimensional filter coefficient generated in S1307 is the same as that shown in FIG. Then, as shown in FIG. 9B, the thinning information is generated using the filter coefficient created in this procedure, so that the thinning information of the pixel where the toner amount becomes maximum becomes large, and the toner amount becomes the standard amount. The thinning information of pixels in the range of “0” becomes “0”. Therefore, by generating the filter coefficient by this procedure, it is possible to reduce the toner amount only for the pixels where the toner amount is excessive due to the phenomenon of sweeping, and to increase the toner reduction amount of the pixel where the toner amount is the most excessive. Can do.

  Hereinafter, a procedure for generating the drive signal 212 subjected to the PWM processing for reducing the toner amount when multi-valued image data stored in the image memory 231 is transmitted to the printer engine will be described. Here, pixels in which the toner amount is excessive due to the edge effect or the phenomenon of sweeping are detected, and a drive signal 212 is generated by performing PWM processing for reducing the toner amount for these pixels.

  As described above, multi-value image data is stored in the image memory 231, and this image data is read out and transmitted to the image processing unit 260 under the control of the CPU 210.

  Here, the density conversion unit 261 and the halftone conversion unit 262 process the multi-valued image data received from the image memory 231 to generate binary image data, and the delay unit 263 and the thinning information generation unit. H.264. Here, the delay unit 263 delays the binary image data received from the halftone conversion unit 262 and transmits it to the thinning information addition unit 265. The thinning information generation unit 264 generates thinning information from the binary image data received from the halftone conversion unit 262 and transmits the thinning information to the thinning information addition unit 265. The thinning information adding unit 265 generates binary image data with thinning information by combining the binary image data received from the delay unit 263 and the thinning information received from the thinning information generation unit 264. Stored in the image memory 231.

  Thus, the binary image data with the thinning information stored in the image memory 231 is transmitted to the exposure driving unit 250 under the control of the CPU 210. The exposure driving unit 250 generates a drive signal 212 in which the image density is adjusted by PWM control based on the binary image data with thinning information received from the image memory 231, and outputs the drive signal 212 to the exposure apparatus 130.

  As described above, when multi-valued image data stored in the image memory 231 is transmitted to the printer engine, a pixel whose toner amount is excessive due to an edge effect or a phenomenon of sweeping is detected. The procedure for generating the drive signal 212 that has been subjected to PWM processing for reducing the toner amount for the detected pixel is shown.

  With this procedure, the pixels that have excessive toner amount due to the edge effect and the phenomenon of sweeping and the extent thereof are determined by simple processing based on the characteristics of the printer engine, and only for the pixels with excessive toner amount, Correction processing for reducing the toner amount can be executed.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  The present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 130 ... Exposure apparatus, 210 ... CPU, 211 ... Light quantity adjustment signal, 212 ... Drive signal, 231 ... Image memory, 240 ... Exposure control part, 250 ... Exposure drive part, 260 ... Image processing part

Claims (9)

Image formation comprising: a photoconductor; an exposure device that irradiates the photoconductor with light based on an exposure signal to form an electrostatic latent image on the photoconductor; and a control unit that supplies the exposure signal to the exposure device A device,
The control means includes
A detection means for executing a filtering process on the input image data and detecting a pixel and a toner amount after development exceeding a predetermined amount due to an edge effect or a phenomenon of sweeping;
Based on the detection result of the detection means, create thinning information for determining the pixel to be reduced in toner amount and the amount to be reduced, and create image data with the thinning information added to the image data Creating means to
Generating means for generating the exposure signal based on the image data created by the creating means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein filter coefficients used in the filtering process are different from each other for the edge effect and the sweeping phenomenon.   The filter coefficient has a positive coefficient value of a pixel between the target pixel and a pixel at a first distance from the target pixel, and a coefficient value of a pixel at the first distance from the target pixel is 0. A coefficient value of a peripheral pixel that is equal to or more than the second distance from the target pixel is 0, and a pixel that is the first distance from the target pixel and a pixel that is the second distance away from the target pixel; 3. The image forming apparatus according to claim 1, wherein a coefficient value of a pixel in between is a negative number.   The first distance is a distance from an image end of a pixel in which the toner amount is most excessive due to the edge effect or sweeping phenomenon, and the second distance is the edge effect or sweeping phenomenon. The image forming apparatus according to claim 3, wherein the distance of the pixel whose toner amount returns to a standard range due to the phenomenon is a distance from the image end portion.   5. The exposure apparatus according to claim 1, wherein the photoconductor is irradiated with the light corresponding to a pixel whose pixel value is not 0 by performing pulse width modulation according to the thinning information. The image forming apparatus described in the item.   The image forming apparatus according to claim 5, wherein the image data is image data obtained by binarizing multivalued image data.   The image forming apparatus according to claim 1, further comprising a storage unit that stores the first distance and the second distance. Image formation comprising: a photoconductor; an exposure device that irradiates the photoconductor with light based on an exposure signal to form an electrostatic latent image on the photoconductor; and a control unit that supplies the exposure signal to the exposure device A control method for controlling an apparatus, comprising:
A detection step of performing filter processing on the input image data to detect pixels and the amount of toner after development exceeding a predetermined amount due to an edge effect or a phenomenon of sweeping;
Based on the detection result in the detection step, the thinning information for determining the pixel for which the toner amount is to be reduced and the amount to be reduced is created, and the image data is created by adding the thinning information to the image data. Creating process,
A generating step for generating the exposure signal based on the image data created in the creating step;
A control method for an image forming apparatus, comprising:   A program for causing a computer to function as each unit of the image forming apparatus according to any one of claims 1 to 7.

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